Makefile: Install qemu-[qmp/ga]-ref.* into the directory "interop"

We need install qemu-[qmp/ga]-ref.* files into the subdirectory of qemu docs: interop.

If we visit the following address and click the link to qemu-qmp-ref.html:
https://www.qemu.org/docs/master/interop/bitmaps.html#basic-qmp-usage

It will report following error:
"
Not Found
The requested URL /docs/master/interop/qemu-qmp-ref.html was not found on this server.
"
Signed-off-by: NLiao Pingfang <liao.pingfang@zte.com.cn>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <1591663670-47712-1-git-send-email-wang.yi59@zte.com.cn>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -873,8 +873,9 @@ install-sphinxdocs: sphinxdocs
 install-doc: $(DOCS) install-sphinxdocs
 	$(INSTALL_DIR) "$(DESTDIR)$(qemu_docdir)"
 	$(INSTALL_DATA) $(MANUAL_BUILDDIR)/index.html "$(DESTDIR)$(qemu_docdir)"
-	$(INSTALL_DATA) docs/interop/qemu-qmp-ref.html "$(DESTDIR)$(qemu_docdir)"
-	$(INSTALL_DATA) docs/interop/qemu-qmp-ref.txt "$(DESTDIR)$(qemu_docdir)"
+	$(INSTALL_DIR) "$(DESTDIR)$(qemu_docdir)/interop"
+	$(INSTALL_DATA) docs/interop/qemu-qmp-ref.html "$(DESTDIR)$(qemu_docdir)/interop"
+	$(INSTALL_DATA) docs/interop/qemu-qmp-ref.txt "$(DESTDIR)$(qemu_docdir)/interop"
 ifdef CONFIG_POSIX
 	$(INSTALL_DIR) "$(DESTDIR)$(mandir)/man1"
 	$(INSTALL_DATA) $(MANUAL_BUILDDIR)/system/qemu.1 "$(DESTDIR)$(mandir)/man1"
@@ -892,8 +893,9 @@ ifdef CONFIG_TRACE_SYSTEMTAP
 endif
 ifneq (,$(findstring qemu-ga,$(TOOLS)))
 	$(INSTALL_DATA) $(MANUAL_BUILDDIR)/interop/qemu-ga.8 "$(DESTDIR)$(mandir)/man8"
-	$(INSTALL_DATA) docs/interop/qemu-ga-ref.html "$(DESTDIR)$(qemu_docdir)"
-	$(INSTALL_DATA) docs/interop/qemu-ga-ref.txt "$(DESTDIR)$(qemu_docdir)"
+	$(INSTALL_DIR) "$(DESTDIR)$(qemu_docdir)/interop"
+	$(INSTALL_DATA) docs/interop/qemu-ga-ref.html "$(DESTDIR)$(qemu_docdir)/interop"
+	$(INSTALL_DATA) docs/interop/qemu-ga-ref.txt "$(DESTDIR)$(qemu_docdir)/interop"
 	$(INSTALL_DATA) docs/interop/qemu-ga-ref.7 "$(DESTDIR)$(mandir)/man7"
 endif
 endif

docs/index.html.in

@@ -12,8 +12,8 @@
             <li><a href="tools/index.html">Tools Guide</a></li>
             <li><a href="interop/index.html">System Emulation Management and Interoperability Guide</a></li>
             <li><a href="specs/index.html">System Emulation Guest Hardware Specifications</a></li>
-            <li><a href="qemu-qmp-ref.html">QMP Reference Manual</a></li>
-            <li><a href="qemu-ga-ref.html">Guest Agent Protocol Reference</a></li>
+            <li><a href="interop/qemu-qmp-ref.html">QMP Reference Manual</a></li>
+            <li><a href="interop/qemu-ga-ref.html">Guest Agent Protocol Reference</a></li>
         </ul>
     </body>
 </html>